1. Field of the Invention
This invention relates to a valve and more particularly to a rotary valve having a bent valve stem enclosed and hermetically sealed by a bent bellows which is internally pressurized during operation of the valve and supported substantially along its entire length by the valve stem to resist lateral deflection and distortion of the bellows and thereby prevent failure of the bellows seal.
2. Description of the Prior Art
In rotary valves, such as butterfly, ball, plug and the like, for conveyance of fluids and particularly contaminated fluids at high pressure, as well as at substantially reduced pressure or under vacuum conditions, it is preferred to utilize static seals as opposed to packed or dynamic seals. Packed or dynamic seals are subject to wear resulting in valve leakage, particularly at the pressure boundary between the valve stem and the valve member. A commonly used static seal is a bellows surrounding the valve stem. U.S. Pat. Nos. 1,644,825; 2,659,569; 2,659,570 and 3,811,651 disclose rotary valves that utilize a bellows for sealing around the valve stem between the valve actuator and the valve member.
Conventionally, a bellows, when used to seal a valve stem, is bonded or welded to the structure of the valve body that supports the rotatable valve member at one end and at the opposite end to a retainer or cap that connects the valve stem to the valve actuator. This arrangement is illustrated in U.S. Pat. No. 3,811,651. Because the connections at the ends of the bellows are metal-to-metal, a static seal is formed. It is known to laterally deflect the valve stem or utilize a crank-like valve stem and hermetically seal the stem in the bellows. In this manner, the valve stem connects the actuator to the valve member to prevent torsional loading of the bellows, as illustrated in U.S. Pat. Nos. 1,644,825 and 3,811,651.
One of the difficulties encountered with a bent valve stem hermetically sealed in a bellows of the type described above is that the bellows must also bend in order to enclose the valve. Thus, the bellows is initially flexed and therefore is subject to lateral distortion or "squirming". A bellows by its flexible nature when subjected to axial compression tends to deflect laterally or "squirm". This will occur at relatively low forces.
When a bellows is internally pressurized, the pressure applied to the inside of the bellows around the valve stem tends to outwardly deflect the bellows. Therefore, a bellows is subject to failure to a much greater degree when subjected to internal pressure and laterally deflected. This problem is magnified when the bellows is initially flexed or heat.
While it has been suggested by the prior art devices to use a bellows to hermetically seal a valve stem particularly as a static seal around a bent valve stem, a bent bellows in unstable and therefore subject to distortion and consequent bellows failure. Therefore, there is a need in non-rising rotary valves for a bent bellows valve seal which is supported to resist lateral deflection when the bellows is internally pressurized and prevent bellows failure.